Browsing by Author "Ozdemir, Resul"

Now showing 1 - 16 of 16

Ambipolar small molecular semiconductor-based heterojunction diode
(ELSEVIER SCIENCE SAPO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2016) Ocaya, R. O.; Ozdemir, Mehmet; Ozdemir, Resul; Al-Ghamdi, Ahmed; Usta, Hakan; Farooq, W. A.; Yakuphanoglu, F.; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Ozdemir, Resul
A heterojunction diode based on an ambipolar organic semiconductor 2,8-bis(5-(2-octyldodecyl)thien-2-yl)indeno[1,2-b]fluorene-6,12-dione (20D-TIFDKT) was fabricated on p-Si using a drop-casting technique. The current-voltage and capacitance-voltage characteristics of Al/20D-TIFDKT/p-Si/Al devices with aluminized contacts were investigated under dark and 100 mW/cm(2) illumination intensity. The result is a novel interface-state controlled diode device that is shown to be rectifying. In the forward, bias it has a current that depends on the illumination intensity at constant bias, showing potential application in low-power solar cell application. In the reverse bias, it has a response that depends on the illumination intensity regardless of the applied reverse bias. This suggests a potential use as a sensor in photoconductive applications. Between 0 and 0.7 V forward bias, the ideality factor, series resistance and barrier height average at 2.35, 67.6 k Omega and 0.842 eV, respectively, regardless of illumination. (C) 2016 Elsevier B.V. All rights reserved.
BODIPY-Based Semiconducting Materials for Organic Bulk Heterojunction Photovoltaics and Thin-Film Transistors
(WILEY-V C H VERLAG GMBH, POSTFACH 101161, 69451 WEINHEIM, GERMANY, 2019) Ho, Dongil; Ozdemir, Resul; Kim, Hyungsug; Earmme, Taeshik; Usta, Hakan; Kim, Choongik; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
The rapid emergence of organic (opto)electronics as a promising alternative to conventional (opto)electronics has been achieved through the design and development of novel pi-conjugated systems. Among various semiconducting structural platforms, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) pi-systems have recently attracted attention for use in organic thin-films transistors (OTFTs) and organic photovoltaics (OPVs). This Review article provides an overview of the developments in the past 10 years on the structural design and synthesis of BODIPY-based organic semiconductors and their application in OTFT/OPV devices. The findings summarized and discussed here include the most recent breakthroughs in BODIPYs with record-high charge carrier mobilities and power conversion efficiencies (PCEs). The most up-to-date design rationales and discussions providing a strong understanding of structure-property-function relationships in BODIPY-based semiconductors are presented. Thus, this review is expected to inspire new research for future materials developments/applications in this family of molecules.
A dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT)-based hole transporting layer for highly stable perovskite solar cells with efficiency over 22%
(ROYAL SOC CHEMISTRY, 2022) Kaya, Ismail Cihan; Ozdemir, Resul; Usta, Hakan; Sonmezoglu, Savas; 0000-0002-7957-110X; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Özdemir, Resul; Usta, Hakan
In this study, for the first time, n-i-p PSCs were fabricated using dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) as the solution-processed hole transporting layer (HTL). The power conversion efficiency (PCE) of the optimized device with the C8-BTBT film that favored edge-on molecular alignment was 22.45% with negligible hysteresis. A thinner dopant-free C8-BTBT HTL effectively protected the perovskite layer from moisture resulting in better shelf-life stability for un-encapsulated PSCs, which maintained >80% of its initial PCE (after a period of 120 days) at a relative humidity level of 40-45%. In addition, the C8-BTBT-based PSCs kept their high performance with no obvious PCE loss at 60 degrees C for 20 days in the ambient atmosphere and retained 82% of their initial PCE at 85 degrees C for 10 days. Overall, our findings revealed that a thin solution-processed C8-BTBT HTL plays a critical role not only in hole extraction and transport but also in greatly improving the ambient and thermal stability of n-i-p PSCs.
Engineering functionalized low LUMO [1]benzothieno[3,2-b][1]benzothiophenes (BTBTs): unusual molecular and charge transport properties
(ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2020) Ozdemir, Resul; Ahn, Kyunghan; Deneme, Ibrahim; Zorlu, Yunus; Kim, Dojun; Kim, Myung-Gil; Usta, Hakan; 0000-0002-7957-110X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Diacene-fused thienothiophenes (DAcTTs) have provided an excellent pi-framework for the development of high mobility p-type molecular semiconductors in the past decade. However, n-type DAcTTs are rare and their electron transport characteristics remain largely unexplored. Herein, a series of functionalized low LUMO (lowest unoccupied molecular orbital) [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based small molecules, D(C7CO)-BTBT, C7CO-BTBT-CC(CN)(2)C-7, and D(C7CC(CN)(2))-BTBT, have been developed. Detailed structural, physicochemical, optoelectronic, and single-crystal characterization were performed. The new molecules exhibit large optical band gaps (similar to 2.8-3.1 eV) and highly stabilized (-Delta E-LUMO = 1.2-1.4 eV)/pi-delocalized LUMOs as compared to p-type DAcTTs. Symmetric functionalization is found to be important to enable strong intermolecular interactions in the solid-state. All molecules exhibit alternately stacked layers of "F-BTBT-F" and "S" (F: functional group/S: substituent) with strong herringbone-like interactions (2.8-3.6 angstrom distances) between pi-cores. While carbonyls, regardless of the substituent, adopt nearly coplanar pi-backbones with BTBT, dicyanovinylenes are found to be twisted (47.5 degrees). The conformational difference at the molecular level has unusual effects on the pi-electron deficiencies, frontier molecular orbital energetics, thermal/photophysical properties, and pi-electronic structures. Dicyanovinylenes at the 2,7 positions, despite twisted conformations, are shown for the first time to yield good electron transport in DAcTTs. The D(C7CC(CN)(2))-BTBT thin film exhibits large 2D plate-like crystalline grains (similar to 1-2 mu m sizes) of terraced islands and becomes a rare example of an n-type DAcTT in organic field-effect transistors (OFETs). Although a stabilized/pi-delocalized LUMO, largely governed by functional groups and intramolecular twists, is essential for electron transport, our findings suggest that it should be combined with proper substituents to yield a favorable three-dimensional BTBT/functional group pi-electronic structure and a low intramolecular reorganization energy. Combined with our first n-type DAcTT semiconductor D(PhFCO)-BTBT, a molecular library with systematically varied chemical structures has been studied herein for the first time for low LUMO DAcTTs. The molecular engineering perspectives presented in this study may give unique insights into the design of novel electron transporting thienoacenes for unconventional optoelectronics.
Frequency and electric field controllable photodevice: FYTRONIX device
(ELSEVIERRADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2017) Tataroglu, A.; Al-Sehemi, Abdullah G.; Ozdemir, Mehmet; Ozdemir, Resul; Usta, Hakan; Al-Ghamdi, Ahmed A.; Farooq, W. A.; Yakuphanoglu, F.; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Ozdemir, Resul; Usta, Hakan
Al/p-Si/BODIPY/Al diode was fabricated by forming BODIPY organic layer on p-Si having ohmic contact. The electrical and photoresponse properties of the prepared diode were investigated in detail. The current-voltage ( I-V) measurements were performed under dark and various illumination intensities. It is observed that the photocurrent under illumination is higher than the dark current. The transient measurements indicate that the device exhibits both photodiode and photocapacitor behavior. We called this device as FYTRONIX device. The photoresponse behavior of the FYTRONIX device is controlled simultaneously by frequency and electric field. The FYRONIX device can be used as a photoresponse sensor in optoelectronic applications.
High Electron Mobility in [1]Benzothieno[3,2-b][1]benzothiophene-Based Field-Effect Transistors: Toward n-Type BTBTs
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2019) Usta, Hakan; Kim, Dojeon; Ozdemir, Resul; Zorlu, Yunus; Kim, Sanghyo; Ruiz Delgado, M. Carmen; Harbuzaru, Alexandra; Kim, Seonhyoung; Demirel, Gokhan; Hong, Jongin; Ha, Young-Geun; Cho, Kilwon; Facchetti, Antonio; Kim, Myung-Gil; 0000-0002-2891-5785; 0000-0003-2811-1872; 0000-0002-7957-110X; 0000-0002-8211-732X; 0000-0002-0618-1979; 0000-0002-9778-917X; 0000-0003-2434-3182; 0000-0001-8180-7153; 0000-0001-9632-3557; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The first example of an n-type [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based semiconductor, D-(PhFCO)-BTBT, has been realized via a two-step transition metal-free process without using chromatographic purification. Physicochemical and optoelectronic characterizations of the new semiconductor were performed in detail, and the crystal structure was accessed. The new molecule exhibits a large optical band gap (similar to 2.9 eV) and highly stabilized (Delta E-LUMO = 1.54 eV)/pi-delocalized lowest unoccupied molecular orbital (LUMO) mainly comprising the BTBT pi-core and in-plane carbonyl units. The effect of out-of-plane twisted (64 degrees) pentafluorophenyl groups on LUMO stabilization is found to be minimal. Polycrystalline D(PhFCO)-BTBT thin films prepared by physical vapor deposition exhibited large grains (similar to 2-5 mu m sizes) and "layer-by-layer" stacked edge-on oriented molecules with an in-plane herringbone packing (intermolecular distances similar to 3.25-3.46 angstrom) to favor two-dimensional (2D) source-to-drain (S -> D) charge transport. The corresponding TC/BG-OFET devices demonstrated high electron mobilities of up to similar to 0.6 cm(2)/V.s and I-on/I-off ratios over 10(7)-10(8). These results demonstrate that the large band gap BTBT pi-core is a promising candidate for high-mobility n-type organic semiconductors and, combination of very large intrinsic charge transport capabilities and optical transparency, may open a new perspective for next-generation unconventional (opto)electronics.
Highly Efficient Deep-Blue Electroluminescence Based on a Solution-Processable A-pi-D-pi-A Oligo(p-phenyleneethynylene) Small Molecule
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2019) Usta, Hakan; Alimli, Dilek; Ozdemir, Resul; Dabak, Salih; Zorlu, Yunus; Alkan, Fahri; Tekin, Emine; Can, Ayse; 0000-0002-7957-110X; 0000-0002-0618-1979; 0000-0003-4564-9447; 0000-0003-2811-1872; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The development of solution-processable fluorescent small molecules with highly efficient deep-blue electroluminescence is of growing interest for organic light-emitting diode (OLED) applications. However, high-performance deep-blue fluorescent emitters with external quantum efficiencies (EQEs) over 5% are still scarce in OLEDs. Herein, a novel highly soluble oligo(p-phenyleneethynylene)-based small molecule, 1,4-bis((2-cyanophenyl)ethynyl)-2,5-bis(2-ethylhexyloxy)benzene (2EHO-CNPE), is designed, synthesized, and fully characterized as a wide band gap (2.98 eV) and highly fluorescent (Phi(PL) = 0.90 (solution) and 0.51 (solid-state)) deep-blue emitter. The new molecule is functionalized with cyano (-CN)/2-ethylhexyloxy (-OCH2CH(C2H5)C4H9) electron-withdrawing/-donating substituents, and ethynylene is used as a pi-spacer to form an acceptor (A)-pi-donor (D)-pi-acceptor (A) molecular architecture with hybridized local and charge transfer (HLCT) excited states. Physicochemical and optoelectronic characterizations of the new emitter were performed in detail, and the single-crystal structure was determined. The new molecule adopts a nearly coplanar pi-conjugated framework packed via intermolecular "C-H center dot center dot center dot pi" and "C-H center dot center dot center dot N" hydrogen bonding interactions without any pi-pi stacking. The OLED device based on 2EHO-CNPE shows an EQE(max) of 7.06% (EQE = 6.30% at 200 cd/m(2)) and a maximum current efficiency (CEmax) of 5.91 cd/A (CE = 5.34 cd/A at 200 cd/m(2)) with a deep-blue emission at CIE of (0.15, 0.09). The electroluminescence performances achieved here are among the highest reported to date for a solution-processed deep-blue fluorescent small molecule, and, to the best of our knowledge, it is the first time that a deep-blue OLED is reported based on the oligo(p-phenyleneethynylene) pi-framework. TDDFT calculations point to facile reverse intersystem crossing (RISC) processes in 2EHO-CNPE from high-lying triplet states to the first singlet excited state (T-2/T-3 -> S-1) (hot-exciton channels) that enable a high radiative exciton yield (eta(r) similar to 69%) breaking the theoretical limit of 25% in conventional fluorescent OLEDs. These results demonstrate that properly designed fluorescent oligo(p-phenyleneethynylenes) can be a key player in high-performance deep-blue OLEDs.
A hybridized local and charge transfer excited state for solution-processed non-doped green electroluminescence based on oligo(p-phenyleneethynylene)
(ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2020) Usta, Hakan; Alimli, Dilek; Ozdemir, Resul; Tekin, Emine; Alkan, Fahri; Kacar, Rifat; Altas, Ahu Galen; Dabak, Salih; Gurek, Ayse Gul; Mutlugun, Evren; Yazici, Ahmet Faruk; Can, Ayse; 0000-0003-4564-9447; 0000-0002-7957-110X; 0000-0003-2747-7856; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
We herein report a new highly efficient green emissive hot-exciton molecule, 1,4-bis((4'-diphenylamino3-cyano-[1,1'-biphenyl]-4-yl)ethynyl)-2,5-bis(2-ethylhexyloxy)benzene (2EHO-TPA-CNPE) that consists of an extended D'-pi'-A-pi-D-pi-A-pi'-D' molecular p-system with diphenylamino end units (D') and ethynylene/phenylene spacers (pi/pi'). The new molecule exhibits high photoluminescence (PL) quantum efficiencies (Phi(PL) = 0.95 (solution) and 0.45 (spin-coated neat thin-film)), and a strong PL solvatochromic behavior revealing significant changes in excited state energies/characteristics (locally excited (LE) -> hybridized local and charge transfer (HLCT) - charge-transfer (CT)) depending on solvent polarity. Highly efficient (radiative exciton yield (eta(r)) = 50-59% >> 25%) green-emitting OLEDs were fabricated in a conventional device architecture by employing (non-)doped thin-films reaching a maximum current efficiency (CEmax) of 12.0 cd A(-1) and a maximum external quantum efficiency (EQE(max)) of 5.5%. The emission profile of the non-doped OLED has CIE 1976 (u', v') chromaticity coordinates of (0.10, 0.55) corresponding to a night vision imaging system (NVIS) compatible Green A region. 2EHO-TPA-CNPE-based OLED devices of industrial relevance were also fabricated by ink-jet printing the emissive layer and by fabricating an inverted architecture, which possessed respectable device performances of 2.4-6.1 cd A(-1). The solid-state solvation effect in OLED devices yields HLCT electronic behavior resulting in high Zr's, which is confirmed by TDDFT to originate from energetically/spatially favorable reverse intersystem crossings (RISCs) (T-2/3 -> S-1). As a unique observation, delayed fluorescence due to this RISC was evident in the PL decay lifetime measurement with a ns-scale lifetime of similar to 10 ns. These results clearly allow a better understanding of the structure-photophysical property-electroluminescence relationships in this new class of oligo(p-phenyleneethynylene)-based hot-exciton molecules, and it could open up new opportunities for high-performance solution-processed optoelectronic/sensing applications.
Meso-pi-Extended/Deficient BODIPYs and Low-Band-Gap Donor-Acceptor Copolymers for Organic Optoelectronics
(AMER CHEMICAL SOC, 2022) Can, Ayse; Choi, Gi-Seok; Ozdemir, Resul; Park, Soyoon; Park, Jin Su; Lee, Yongchul; Deneme, Ibrahim; Mutlugun, Evren; Kim, Choongik; Kim, Bumjoon J.; Usta, Hakan; 0000-0002-7957-110X; 0000-0003-3715-5594; 0000-0002-0618-1979; 0000-0001-9415-0242; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Can, Ayse; Ozdemir, Resul; Mutlugun, Evren; Deneme, Ibrahim; Usta, Hakan
The realization of π-deficient acceptors and their donor− acceptor copolymers has become a key research focus for the realization of versatile organic optoelectronic materials and devices. Herein, we demonstrate the theoretical design, synthesis, and physicochemical/ optoelectronic characterization of two meso-π-extended/deficient BODIPY building blocks (2OD−T2BDY and 2OD−TTzBDY) and a library of donor−acceptor copolymers with low band gap (Eg = 1.30−1.35 eV) based on these building blocks. These building blocks, to the best of our knowledge, are the first examples of BODIPYs with meso-π-extension. A library of BODIPY building blocks with varied meso units/substituents is studied to reveal the meso effects on the semiconducting BODIPY’s optoelectronic properties. The building blocks showed favorable πacceptor electronic/structural properties with meso-π-delocalized and stabilized LUMOs (ca. −3.6 eV) and large ground-state dipole moments of 4.9−5.5 D. Consistent with the theoretical/experimental π-electronic structures, all copolymers functioned as p-type semiconductors in field-effect transistors and as donor materials in the bulk heterojunction organic photovoltaics. Power conversion efficiencies of up to 4.4% with a short-circuit current of 12.07 mA cm−2 were achieved. This study demonstrates a unique meso-πextension strategy to realize BODIPYs with favorable π-acceptor properties, and our findings could open up future materials design avenues in various organic optoelectronic applications.
Molecular engineering of organic semiconductors enables noble metal-comparable SERS enhancement and sensitivity
(NATURE PUBLISHING GROUP, MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND, 2019) Demirel, Gokhan; Gieseking, Rebecca L. M.; Ozdemir, Resul; Kahmann, Simon; Loi, Maria A.; Schatz, George C.; Facchetti, Antonio; Usta, Hakan; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
Nanostructured molecular semiconductor films are promising Surface-Enhanced Raman Spectroscopy (SERS) platforms for both fundamental and technological research. Here, we report that a nanostructured film of the small molecule DFP-4T, consisting of a fully pi-conjugated diperfluorophenyl-substituted quaterthiophene structure, demonstrates a very large Raman enhancement factor (>10(5)) and a low limit of detection (10(-9) M) for the methylene blue probe molecule. This data is comparable to those reported for the best inorganic semiconductor- and even intrinsic plasmonic metal-based SERS platforms. Photoluminescence spectroscopy and computational analysis suggest that both charge-transfer energy and effective molecular interactions, leading to a small but non-zero oscillator strength in the charge-transfer state between the organic semiconductor film and the analyte molecule, are required to achieve large SERS enhancement factors and high molecular sensitivities in these systems. Our results provide not only a considerable experimental advancement in organic SERS figure-of-merits but also a guidance for the molecular design of more sensitive SERS systems.
Organic and inorganic semiconducting materials-based SERS: recent developments and future prospects
(Royal Society of Chemistry, 2024) Ozdemir, Resul; Ozkan Hukum, Kubra; Usta, Hakan; Demirel, Gokhan; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Surface-enhanced Raman spectroscopy (SERS) with high sensitivity/selectivity is a powerful analytical tool and has been widely used, particularly in the fields of chemistry, spectroscopy, molecular detection, food safety, anti-counterfeiting, and environmental monitoring. Conventional SERS detection relies on plasmonic materials (e.g., Au and Ag nanostructures) with exceedingly high enhancement factors up to 1012. However, these substrates encounter significant limitations, including poor reproducibility, high cost, lack of selectivity, limited SERS active area leading to inconsistent field enhancement and SERS signals, and the possibility of the photothermal decomposition of the analyte species. These drawbacks have the potential to impede detection accuracy and hinder large-scale practical applications. This review focuses on alternative approaches based on noble metal-free SERS substrates. Considering recent advancements in the field of SERS active platforms, we first introduce the implementation of inorganic compounds, including metal oxides, transition metal sulfides/-selenides/-tellurides, 2-D layered transition metal carbides and nitrides (Mxenes), metal-organic frameworks (MOFs), and single elemental inorganic materials for Raman signal enhancement applications. In the second part of the review, we highlight the fast-growing field of SERS-active organic platforms. Moreover, we discuss the promises and challenges for the future direction of organic and inorganic material-based SERS.
Organic Light-Emitting Physically Unclonable Functions
(WILEY-V C H VERLAG GMBHPOSTFACH 101161, 69451 WEINHEIM, GERMANY, 2021) Kayaci, Nilgun; Ozdemir, Resul; Kalay, Mustafa; Kiremitler, N. Burak; Usta, Hakan; Onses, M. Serdar; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Resul; Usta, Hakan
The development of novel physically unclonable functions (PUFs) is of growing interest and fluorescent organic semiconductors (f-OSCs) offer unique advantages of structural versatility, solution-processability, ease of processing, and great tuning ability of their physicochemical/optoelectronic/spectroscopic properties. The design and ambient atmosphere facile fabrication of a unique organic light-emitting physically unclonable function (OLE-PUF) based on a green-emissive fluorescent oligo(p-phenyleneethynylene) molecule is reported. The OLE-PUFs have been prepared by one-step, brief (5 min) thermal annealing of spin-coated nanoscopic films (approximate to 40 nm) at a modest temperature (170 degrees C), which results in efficient surface dewetting to form randomly positioned/sized hemispherical features with bright fluorescence. The random positioning of molecular domains generated the unclonable surface with excellent uniformity (0.50), uniqueness (0.49), and randomness (p > 0.01); whereas the distinctive photophysical and structural properties of the molecule created the additional security layers (fluorescence profile, excited-state decay dynamics, Raman mapping/spectrum, and infrared spectrum) for multiplex encoding. The OLE-PUFs on substrates of varying chemical structures, surface energies and flexibility, and direct deposition on goods via drop-casting are demonstrated. The OLE-PUFs immersed in water, exposed to mechanical abrasion, and read-out repeatedly via fluorescence imaging showed great stability. These findings clearly demonstrate that rationally engineered solution-processable f-OSCs have a great potential to become a key player in the development of new-generation PUFs.
A Solution-Processable Liquid-Crystalline Semiconductor for Low-Temperature-Annealed Air-Stable N-Channel Field-Effect Transistors
(WILEY-V C H VERLAG GMBHPOSTFACH 101161, 69451 WEINHEIM, GERMANY, 2017) Ozdemir, Resul; Choi, Donghee; Ozdemir, Mehmet; Kim, Hyekyoung; Kostakoglu, Sinem Tuncel; Erkartal, Mustafa; Kim, Hyungsug; Kim, Choongik; Usta, Hakan; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Resul; Ozdemir, Mehmet; Erkartal, Mustafa; Usta, Hakan
A new solution-processable and air-stable liquid-crystalline nchannel organic semiconductor (2,2'-(2,8-bis(5-(2-octyldodecyl) thiophen-2-yl) indeno[1,2-b] fluorene-6,12-diylidene) dimalononitrile, alpha,omega-2OD-TIFDMT) with donor-acceptor-donor (D-AD) pi conjugation has been designed, synthesized, and fully characterized. The new semiconductor exhibits a low LUMO energy (-4.19 eV) and a narrow optical bandgap (1.35 eV). The typical pseudo-focal-conic fan-shaped texture of a hexagonal columnar liquid-crystalline (LC) phase was observed over a wide temperature range. The spin-coated semiconductor thin films show the formation of large (approximate to 0.5-1 mu m) and highly crystalline platelike grains with edge-on molecular orientations. Low-temperature-annealed (50 degrees C) top-contact/bottom-gate OFETs have provided good electron obility values as high as 0.11 cm(2) (Vs)(-1) and high I-on/I-off ratios of 10(7) to 10(8) with excellent ambient stability. This indicates an enhancement of two orders of magnitude (100 V) when compared with the b-substituted parent semiconductor, beta-DD-TIFDMT (2,2'-(2,8-bis(3-dodecylthiophen- 2-yl) indeno[1,2-b] fluorene-6,12-diylidene) dimalononitrile). The current rational alkyl-chain engineering route offers great advantages for D-A-D pi-core coplanarity in addition to maintaining good solubility in organic solvents, and leads to favorable optoelectronic/physicochemical characteristics. These remarkable findings demonstrate that alpha,omega-2OD-TIFDMT is a promising semiconductor material for the development of n-channel OFETs on flexible plastic substrates and LC-state annealing of the columnar liquid crystals can lower the electron mobility for transistor-type charge transport.
A Solution-Processable meso-Phenyl-BODIPY-Based n-Channel Semiconductor with Enhanced Fluorescence Emission
(WILEY-V C H VERLAG GMBH, POSTFACH 101161, 69451 WEINHEIM, GERMANY, 2019) Ozcan, Emrah; Ozdemir, Mehmet; Ho, Dongil; Zorlu, Yunus; Ozdemir, Resul; Kim, Choongik; Usta, Hakan; Cosut, Bunyemin; 0000-0002-0618-1979; 0000-0002-7957-110X; 0000-0001-6530-0205; 0000-0001-6325-5674; 0000-0003-2811-1872; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The cover feature shows the delicate balance between locally excited (LE) and twisted intramolecular charge-transfer (TICT) states, which could be controlled by solvent polarity and nano-aggregation, of a meso-phenyl-BODIPY-based fluorescent semiconductor. The dihedral angle between the meso-aromatic unit and BODIPY pi-core was found to be the key factor in this balance. This is the first report of highly emissive characteristics for an A-D-A type BODIPY-based n-channel semiconductor. Details are given in the Full Paper by B. Cosut, H. Usta, C. Kim, and co-workers (DOI: 10.1002/cplu.201900317).
Trans-cis isomerization assisted synthesis of solution-processable yellow fluorescent maleic anhydrides for white-light generation
(ELSEVIER, 2015) Ozdemir, Mehmet; Genc, Sinan; Ozdemir, Resul; Altintas, Yemliha; Citir, Murat; Sen, Unal; Mutlugun, Evren; Usta, Hakan; 0000-0003-3736-5049; 0000-0002-6909-723X; 0000-0002-0618-1979; 0000-0002-7957-110X; 0000-0002-6666-4980; 0000-0001-5790-2943; 0000-0003-3715-5594; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Genc, Sinan; Ozdemir, Resul; Altintas, Yemliha; Citir, Murat; Sen, Unal; Mutlugun, Evren; Usta, Hakan
Heterocyclic maleic anhydride derivatives have been extensively studied in natural products chemistry over the past few decades. However, their incorporation into optoelectronic devices has lagged behind that of other pi-conjugated systems, and they have never been studied in white light emitting diodes (WLEDs). The development of emissive pi-conjugated materials for (WLEDs) has been an emerging scientific and technological research area to replace phosphors used in LED-based solid-state lighting. Here, we demonstrate the design, synthesis and characterization of two new highly emissive alkyl-substituted bis(thienyl)maleic anhydrides (C6-Th2MA and C12-Th2MA) with favorable photophysical properties. The new core is synthesized via a novel trans-to-cis isomerization-assisted one-pot reaction, which is demonstrated for the first time in the literature for the synthesis of a bis(heteroaryl)maleic anhydride. Due to its favorable absorption and fluorescence properties in the blue and yellow region of the visible spectrum, respectively, C12-Th2MA is studied as a potential wavelength-upconverting material. A WLED fabricated by drop-casting a polymeric solution of C12-Th2MA on a blue LED (InGaN, 455 nm) yields promising CIE coordinates and color-rendering index (CRI) values of (0.24, 0.20) and 65.0, respectively. Considering the simplicity of the current molecular structure and facile synthesis, alkyl-substituted bis(thienyl)maleic anhydrides stand as ideal phosphor alternatives. Therefore, the current findings may open new perspectives for the development of maleic anhydride-based small molecules for low-cost, energy-efficient, and solution-processed lighting technologies. (C) 2015 Elsevier B.V. All rights reserved.
Ultralow bandgap molecular semiconductors for ambient-stable and solution-processable ambipolar organic field-effect transistors and inverters By
(ROYAL SOC CHEMISTRYTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2017) Ozdemir, Resul; Choi, Donghee; Ozdemir, Mehmet; Kwon, Guhyun; Kim, Hyekyoung; Sen, Unal; Kim, Choongik; Usta, Hakan; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The design and development of novel ambipolar semiconductors is very crucial to advance various optoelectronic technologies including organic complementary (CMOS) integrated circuits. Although numerous high-performance ambipolar polymers have been realized to date, small molecules have been unable to provide high ambipolar performance in combination with ambient-stability and solution-processibility. In this study, by implementing highly p-electron deficient, ladder-type IFDK/IFDM acceptor cores with bithiophene donor units in D-A-D pi-architectures, two novel small molecules, 2OD-TTIFDK and 2OD-TTIFDM, were designed, synthesized and characterized in order to achieve ultralow band-gap (1.21-1.65 eV) semiconductors with sufficiently balanced molecular energetics for ambipolarity. The HOMO/LUMO energies of the new semiconductors are found to be -5.47/-3.61 and -5.49/-4.23 eV, respectively. Bottom-gate/top-contact OFETs fabricated via solution-shearing of 2OD-TTIFDM yield perfectly ambient stable ambipolar devices with reasonably balanced electron and hole mobilities of 0.13 cm(2) V-1 s(-1) and 0.01 cm(2) V-1 s(-1), respectively with I-on/I-off ratios of similar to 10(3)-10(4), and 2OD-TTIFDK-based OFETs exhibit ambipolarity under vacuum with highly balanced (mu(e)/mu(h) similar to 2) electron and hole mobilities of 0.02 cm(2) V-1 s(-1) and 0.01 cm(2) V-1 s(-1), respectively with I-on/I-off ratios of similar to 10(5)-10(6). Furthermore, complementary-like inverter circuits were demonstrated with the current ambipolar semiconductors resulting in high voltage gains of up to 80. Our findings clearly indicate that ambient-stability of ambipolar semiconductors is a function of molecular orbital energetics without being directly related to a bulk p-backbone structure. To the best of our knowledge, considering the processing, charge-transport and inverter characteristics, the current semiconductors stand out among the best performing ambipolar small molecules in the OFET and CMOS-like circuit literature. Our results provide an efficient approach in designing ultralow band-gap ambipolar small molecules with good solution-processibility and ambient-stability for various optoelectronic technologies, including CMOS-like integrated circuits.